Redirection of the central metabolism of Klebsiella pneumoniae towards dihydroxyacetone production.

BACKGROUND: Klebsiella pneumoniae is a bacterium that can be used as producer for numerous chemicals. Glycerol can be catabolised by K. pneumoniae and dihydroxyacetone is an intermediate of this catabolism pathway. Here dihydroxyacetone and glycerol were produced from glucose by this bacterium based a redirected glycerol catabolism pathway. RESULTS: tpiA, encoding triosephosphate isomerase, was knocked out to block the further catabolism of dihydroxyacetone phosphate in the glycolysis. After overexpression of a Corynebacterium glutamicum dihydroxyacetone phosphate dephosphorylase (hdpA), the engineered strain produced remarkable levels of dihydroxyacetone (7.0 g/L) and glycerol (2.5 g/L) from glucose. Further increase in product formation were obtained by knocking out gapA encoding an iosenzyme of glyceraldehyde 3-phosphate dehydrogenase. There are two dihydroxyacetone kinases in K. pneumoniae. They were both disrupted to prevent an inefficient reaction cycle between dihydroxyacetone phosphate and dihydroxyacetone, and the resulting strains had a distinct improvement in dihydroxyacetone and glycerol production. pH 6.0 and low air supplement were identified as the optimal conditions for dihydroxyacetone and glycerol production by K, pneumoniae ΔtpiA-ΔDHAK-hdpA. In fed batch fermentation 23.9 g/L of dihydroxyacetone and 10.8 g/L of glycerol were produced after 91 h of cultivation, with the total conversion ratio of 0.97 mol/mol glucose. CONCLUSIONS: This study provides a novel and highly efficient way of dihydroxyacetone and glycerol production from glucose.

Removal of antibiotic resistance genes from swine wastewater by membrane filtration treatment.

Antibiotic resistance genes (ARGs) have attracted extensive attention as an emerging environmental contaminant potentially threatening humans. One of the main emission sources of ARGs is swine wastewater. In this study, integrated membrane filtration including ultrafiltration and two-stage reverse osmosis was conducted for swine wastewater treatment. The abundances of 16 target ARGs, which accounted for 72.64% of the total ARGs in swine wastewater according to metagenomic sequencing, were quantified by quantitative real-time PCR (qPCR) during each stage of the membrane filtration process. The results showed that integrated membrane filtration could reduce more than 99.0% of conventional pollutants and 99.79% of ARGs (from 3.02 × 108 copy numbers/mL to 6.45 × 105 copy numbers/mL). Principal component analysis (PCA) indicated that the removal efficiency of ARGs subtype by membrane filtration did not depend on ARGs type. However, strong correlations were found between ARGs and the wastewater quality indicators TP, SS and EC according to Cooccurrence patterns, indicating that ARG removal was closely associated with insoluble solid particles and soluble ions in swine wastewater. These results showed that membrane filtration could not only remove conventional pollutants such as nitrogen and phosphorus but also reduce the emerging pollutant of ARGs and decrease the risk of ARGs flowing into natural water.

AhlX, an N-acylhomoserine Lactonase with Unique Properties.

N-Acylhomoserine lactonase degrades the lactone ring of N-acylhomoserine lactones (AHLs) and has been widely suggested as a promising candidate for use in bacterial disease control. While a number of AHL lactonases have been characterized, none of them has been developed as a commercially available enzymatic product for in vitro AHL quenching due to their low stability. In this study, a highly stable AHL lactonase (AhlX) was identified and isolated from the marine bacterium Salinicola salaria MCCC1A01339. AhlX is encoded by a 768-bp gene and has a predicted molecular mass of 29 kDa. The enzyme retained approximately 97% activity after incubating at 25 °C for 12 days and ~100% activity after incubating at 60 °C for 2 h. Furthermore, AhlX exhibited a high salt tolerance, retaining approximately 60% of its activity observed in the presence of 25% NaCl. In addition, an AhlX powder made by an industrial spray-drying process attenuated Erwinia carotovora infection. These results suggest that AhlX has great potential for use as an in vitro preventive and therapeutic agent for bacterial diseases.

Production of Chemicals by Klebsiella pneumoniae Using Bamboo Hydrolysate as Feedstock.

Bamboo is an important biomass, and bamboo hydrolysate is used by Klebsiella pneumoniae as a feedstock for chemical production. Here, bamboo powder was pretreated with NaOH and washed to a neutral pH. Cellulase was added to the pretreated bamboo powder to generate the hydrolysate, which contained 30 g/L glucose and 15 g/L xylose and was used as the carbon source to prepare a medium for chemical production. When cultured in microaerobic conditions, 12.7 g/L 2,3-butanediol was produced by wildtype K. pneumoniae. In aerobic conditions, 13.0 g/L R-acetoin was produced by the budC mutant of K. pneumoniae. A mixture of 25.5 g/L 2-ketogluconic acid and 13.6 g/L xylonic acid was produced by the budA mutant of K. pneumoniae in a two-stage, pH-controlled fermentation with high air supplementation. In the first stage of fermentation, the culture was maintained at a neutral pH; after cell growth, the fermentation proceeded to the second stage, during which the culture was allowed to become acidic.

Gluconic acid production by gad mutant of Klebsiella pneumoniae.

Klebsiella pneumoniae produces many economically important chemicals. Using glucose as a carbon source, the main metabolic product in K. pneumoniae is 2,3-butanediol. Gluconic acid is an intermediate of the glucose oxidation pathway. In the current study, a metabolic engineering strategy was used to develop a gluconic acid-producing K. pneumoniae strain. Deletion of gad, resulting in loss of gluconate dehydrogenase activity, led to the accumulation of gluconic acid in the culture broth. Gluconic acid accumulation by K. pneumoniae Δgad was an acid-dependent aerobic process, with accumulation observed at pH 5.5 or lower, and at higher levels of oxygen supplementation. Under all other conditions tested, 2,3-butanediol was the main metabolic product of the process. In fed batch fermentation, a final concentration of 422 g/L gluconic acid was produced by K. pneumoniae Δgad, and the conversion ratio of glucose to gluconic acid reached 1 g/g. The K. pneumoniae Δgad described in this study is the first genetically modified strain used for gluconic acid production, and this optimized method for gluconic acid production may have important industrial applications. Gluconic acid is an intermediate of this glucose oxidation pathway. Deletion of gad, resulting in loss of gluconate dehydrogenase activity, led to the accumulation of gluconic acid in the culture broth. In fed batch fermentation, a final concentration of 422 g/L gluconic acid was produced by the K. pneumoniae Δgad strain, and the conversion ratio of glucose to gluconic acid reached 1 g/g.

Effect of zibushenjing fang on skeletal development and brain tissue antioxidation in mice with kidney essence insufficiency: a mechanistic study.

OBJECTIVE: To investigate the effects of Zibushenjing Fang (formula for tonifying the kidney essence) on skeletal development and brain tissue antioxidation in mice with kidney essence insufficiency. METHODS: Fifty male Kunming mice were randomly divided into five groups: normal group, model group, Jinkuishenqi Wan group, Zibushenjing Fang high dose group, and Zibushenjing Fang low dose group, with 10 mice in each group. The model of kidney essence insufficiency syndrome was established in all the mice except the normal group by using a cat to threaten the mice and by swimming until exhaustion daily which lasted about 21 days. Mice in the model group were administered 20 mL/ kg(-1) x d(-1) of normal saline intragastrically. The Jinkuishenqi Wan group was given 2.7 g/kg(-1) x d(-1) of a solution of Jinkuishenqi Wan. The Zibushenjing Fang high dose group was given 20 g/kg(-1) x d(-1) and the Zibushenjing Fang low dose group was given 10 g/kg(-1) x d(-1) of a solution of Zibushenjing Fang. The general condition of all the groups was observed, including the quantity of food and water intake, swimming time, length of femur, and weight of the femur and musculus quadriceps femoris. The total superoxide dismutase (T-SOD), glutathione peroxidase (GSH-Px), and methane dicarboxylic aldehyde (MDA) activities in the brain tissues were detected. RESULTS: Zibushenjing Fang could improve the manifestation of kidney essence insufficiency, increase the quantity of food and water intake, swimming time, femur length, and femur and musculus quadriceps femoris weight. It could also regulate the activities of T-SOD, GSH-Px, and MDA in brain tissue. CONCLUSION: Zibushenjing Fang may play an important role in treating kidney essence insufficiency syndrome by promoting body development and improving brain tissue antioxidation.

Effect of zibu shenjing fang (see text) on growth and development of the mouse with kidney-essence insufficiency and study on the mechanism.

OBJECTIVE: To investigate effects of Zibu Shenjing Fang (see text) on growth and development of the mouse with insufficiency ofkidney-essence and the mechanism. METHODS: Total 50 mice were randomly divided into a normal group, a model group, a Jingui Shenqi Wan (see text) group, a Zibu Shenjing Fang high dose group and a Zibu Shenjing Fang low dose group, 10 mice in each group. The kidney-essence insufficiency mouse model was established by use of threat-injuring the kidney combined with over-fatigue. At the same time of modeling, the mice in the model group were intragastrically administrated with saline 20 mL x kg(-1) x d(-1), in the Jingui Shenqi Wan group with suspension of the Jingui Shenqi Wan 2.7 g x kg(-1) x d(-1), in the Zibu Shenjing Fang high dose group with Zibu Shenjing Fang 20 g x kg(-1) x d(-1) and in the Zibu Shenjing Fang low dose group with Zibu Shenjing Fang 10 g x kg(-1) x d(-1), for 21 consecutive days. The general state was observed, the body weight was weighted, and serum growth hormone (GH) and insulin-like growth factor-1 (IGF-1) contents were detected. RESULTS: Compared with model group, Zibu Shenjing Fang groups and Jingui Shenqi Wan group could improve manifestation of the mouse with kidney-essence insufficiency, increase body weight of the mouse and serum GH and IGF-1 contents, especially in the high dose group. CONCLUSION: Zibu Shenjing Fang gives play to the function of tonifying the kidney and replenishing essence through regulating GH and IGF-1 levels, so as to influence growth and development of the mouse.